System for additive manufacturing

ABSTRACT

A system is disclosed for additively manufacturing a composite structure. The system may include a support, and a print head connected to and moveable by the support. The print head may have a first tool center point associated with discharge of a first material, and a second tool center point associated with discharge of a second material that is a type different than the first material.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/655,066 that was filed on Oct. 16, 2019, which is based on and claimsthe benefit of priority from U.S. Provisional Application No. 62/751,461that was filed on Oct. 26, 2018, the contents of all of which areexpressly incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and,more particularly, to a system for additively manufacturing compositestructures and a method of operating the system.

BACKGROUND

Automated Fiber Placement (a.k.a., AFP) involves the placement ofpre-impregnated tapes of fibers by a robotically manipulated print head.The fibers can be pre-impregnated with a resin, for example a thermosetresin, partially cured so they can be handled, applied with a backing,and then rolled onto spools in tape form. The tapes are thereafter fedthrough the print head, wherein the backing is removed, and under acompaction roller that presses the tape onto the surface of a mold. Insome applications the substrate (e.g., the surface of the mold or anunderlying layer) can be heated to make it tacky prior to the tapeapplication. After application of the tape is complete, the mold ismoved into an autoclave, where curing of the resin is completed.Although AFP may be an industry standard for manufacturing lightweightand high-strength structures, the process may be expensive, timeconsuming, wasteful, and design-limited.

Continuous fiber 3D printing (a.k.a., CF3D®) may be an improvement overAFP. CF3D® involves the use of continuous fibers that are at leastpartially coated with a matrix inside of a moveable print head, justprior to discharge from the print head. The matrix can be athermoplastic, a thermoset, a powdered metal, or a combination of any ofthese and other known matrixes. Upon exiting the print head, ahead-mounted cure enhancer (e.g., a UV light, an ultrasonic emitter, aheat source, a catalyst supply, etc.) is activated to initiate and/orcomplete curing of the matrix. This curing occurs almost immediately,allowing for unsupported structures to be fabricated in free space,without the need for a mold or an autoclave. An example of thistechnology is disclosed in U.S. Pat. No. 9,511,543 that issued to Tyleron Dec. 6, 2016 (“the '543 patent”). CF3D® may be less expensive,faster, and more efficient than AFP. In addition, CF3D® may have greaterdesign flexibility.

Although CF3D® may have benefits over AFP, synergies be made realizedvia unique combinations of and/or cooperation between AFP and CF3D®components. The disclosed additive manufacturing system and method areuniquely configured to provide these improvements and/or to addressother issues of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a system foradditively manufacturing a composite structure. The system may include asupport, and a print head connected to and moveable by the support. Theprint head may have a first tool center point associated with dischargeof a first material, and a second tool center point associated withdischarge of a second material that is a type different than the firstmaterial.

In another aspect, the present disclosure is directed to a method ofadditively manufacturing a composite structure. The method may includedirecting a reinforcement tape that is pre-impregnated with a matrixpast a heat source to tackify the reinforcement tape, and compacting thetacky reinforcement tape to form a first portion of the compositestructure. The method may further include wetting a reinforcement with amatrix in-situ, compacting the wetted reinforcement to form a secondportion of the composite structure, and at least triggering curing thematrix. The method may further include autoclaving the structure tocomplete curing of the tacky reinforcement tape and the matrix.

In yet another aspect, the present disclosure is directed to anothermethod of additively manufacturing a composite structure. This methodmay include discharging a first material from a print head at a firsttool center point, and discharging a second material that is a typedifferent than the first material from the print head at a second toolcenter point that is different than the first tool center point. Themethod may further include selectively moving the printhead based aknown location of the first tool center point or a known location of thesecond tool center point and desired geometry of the compositestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric illustration of an exemplary disclosed additivemanufacturing system;

FIG. 2 is a cross-sectional illustration of an exemplary print head thatmay be used in conjunction with the additive manufacturing system ofFIG. 1 ;

FIGS. 3 and 4 are isometric illustrations of a structure that may befabricated with the additive manufacturing system of FIG. 1 ; and

FIGS. 5A and 5B are schematic illustrations of an exemplary portion ofthe structures of FIGS. 3 and 4 .

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used tomanufacture a composite structure 12 having any desired shape. System 10may include at least one support 14 and at least one deposition head(“head”) 16. In the disclosed embodiment, two supports 14 areillustrated as independently supporting two different heads 16A and 16B.It is contemplated, however, that a single support 14 couldsimultaneously support both of heads 16A and 16, or that heads 16A and16B could be interchangeably connected to a single support 14, one at atime (e.g., via a tool coupler—not shown).

Heads 16A and 16B may be coupled to and moved by support(s) 14. In thedisclosed embodiment of FIG. 1 , supports 14 are robotic arms (identicalor different arms) capable of moving heads 16A and 16B in multipledirections during fabrication of structure 12. One or both of support(s)14 may alternatively embody an overhead gantry or a hybrid gantry/armalso capable of moving heads 16A and 16B in multiple directions duringfabrication of structure 12. Although supports 14 are shown as beingcapable of 6-axis movements, it is contemplated that supports 14 may becapable of moving heads 16A and 16B in a different manner (e.g., alongor around a greater or lesser number of axes). In some embodiments, adrive may mechanically couple heads 16 to support(s) 14, and includecomponents that cooperate to move portions of and/or supply power ormaterials to head 16.

One or both of heads 16A and 16B may be capable of reaching all requiredportions of structure 12 during fabrication via motion of support(s) 14alone. However, it is contemplated that a moveable part holder 18 may bebeneficial in some embodiments to selectively shuttle structure 12between separate work areas associated with heads 16A and 16B. In thedisclosed embodiment, part holder 18 includes a platform 20 that isslidably mounted to one or more rails 22. In response to a motioncommand, actuators (e.g., motors, pistons, etc.—not shown) associatedwith platform 20 and/or rail(s) 22 may selectively cause the desiredshuttling. It is contemplated that other types of part holders known inthe art could alternatively be utilized to shuttle structure 12 betweenthe separate work areas. In contrast, it is contemplated that structure12 may remain stationary and one or both of supports 14 couldalternatively be associated with rail 22 and configured to slide betweenwork areas. Finally, it is contemplated that part holder 18 and one orboth of supports 14 could be configured to move in a coordinated mannerbetween work areas.

Head 16A may be configured to receive or otherwise contain a matrix(shown as M in FIGS. 1 and 2 ). The matrix may include any type ofmatrix (e.g., a liquid resin, such as a zero-volatile organic compoundresin, a powdered metal, etc.) that is curable. Exemplary resins includethermosets, single- or multi-part epoxy resins, polyester resins,cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics,photopolymers, polyepoxides, thiols, alkenes, thiol-enes, and more. Inone embodiment, the matrix inside head 16A may be pressurized, forexample by an external device (e.g., by an extruder, a pump, etc.—notshown) that is fluidly connected to head 16A via a corresponding conduit(not shown). In another embodiment, however, the pressure may begenerated completely inside of head 16A by a similar type of device. Inyet other embodiments, the matrix may be gravity-fed into and/or throughhead 16. For example, the matrix may be fed into head 16A, and pushed orpulled out of head 16A along with one or more continuous reinforcements(shown as R in FIGS. 1 and 2 ). In some instances, the matrix insidehead 16A may need to be kept cool and/or dark in order to inhibitpremature curing or otherwise obtain a desired rate of curing afterdischarge. In other instances, the matrix may need to be kept warmand/or illuminated for similar reasons. In either situation, head 16Amay be specially configured (e.g., insulated, temperature-controlled,shielded, etc.) to provide for these needs.

The matrix may be used to coat any number of continuous reinforcements(e.g., separate fibers, tows, rovings, socks, and/or sheets ofcontinuous material) and, together with the reinforcements, make up aportion (e.g., a wall) of composite structure 12. The reinforcements maybe stored within (e.g., on one or more separate internal spools) orotherwise passed through head 16A (e.g., fed from one or more externalspools). When multiple reinforcements are simultaneously used, thereinforcements may be of the same material composition and have the samesizing and cross-sectional shape (e.g., circular, square, rectangular,etc.), or a different material composition with different sizing and/orcross-sectional shapes. The reinforcements may include, for example,carbon fibers, vegetable fibers, wood fibers, mineral fibers, glassfibers, metallic wires, optical tubes, plastic fibers (e.g., UHMWPE),etc. It should be noted that the term “reinforcement” is meant toencompass both structural and non-structural types (e.g., functionaltypes) of continuous materials that are at least partially encased inthe matrix discharging from head 16.

The reinforcements may be exposed to (e.g., at least partially coatedwith) the matrix while the reinforcements are inside head 16A, while thereinforcements are being passed to head 16A, and/or while thereinforcements are discharging from head 16A. The matrix, dry (e.g.,unimpregnated) reinforcements, and/or reinforcements that are alreadyexposed to the matrix may be transported into head 16A in any mannerapparent to one skilled in the art. In some embodiments, a fillermaterial (e.g., chopped fibers) may be mixed with the matrix beforeand/or after the matrix coats the continuous reinforcements.

One or more cure enhancers (e.g., a UV light, an ultrasonic emitter, alaser, a heater, a catalyst dispenser, etc.) 23 may be mounted proximate(e.g., within, on, and/or adjacent) head 16A and configured to enhance acure rate and/or quality of the matrix as it is discharged from head16A. Cure enhancer 23 may be controlled to selectively expose portionsof structure 12 to energy (e.g., UV light, electromagnetic radiation,vibrations, heat, a chemical catalyst, etc.) during material dischargeand the formation of structure 12. The energy may trigger a chemicalreaction to occur within the matrix, increase a rate of the chemicalreaction, sinter the matrix, harden the matrix, or otherwise cause thematrix to cure as it discharges from head 16. The amount of energyproduced by cure enhancer 23 may be sufficient to cure the matrix beforestructure 12 axially grows more than a predetermined length away fromhead 16. In one embodiment, structure 12 is completely cured before theaxial growth length becomes equal to an external diameter of thematrix-coated reinforcement.

The matrix and/or reinforcement may be discharged from head 16A via atleast two different modes of operation. In a first mode of operation,the matrix and/or reinforcement are extruded (e.g., pushed underpressure and/or mechanical force) from head 16A as head 16A is moved bysupport 14 to create features of structure 12. In a second mode ofoperation, at least the reinforcement is pulled from head 16A, such thata tensile stress is created in the reinforcement during discharge. Inthis mode of operation, the matrix may cling to the reinforcement andthereby also be pulled from head 16A along with the reinforcement,and/or the matrix may be discharged from head 16A under pressure alongwith the pulled reinforcement. In the second mode of operation, wherethe matrix is being pulled from head 16A with the reinforcement, theresulting tension in the reinforcement may increase a strength ofstructure 12 (e.g., by aligning the reinforcements, inhibiting buckling,etc.), while also allowing for a greater length of unsupported structure12 to have a straighter trajectory. That is, the tension in thereinforcement remaining after curing of the matrix may act against theforce of gravity (e.g., directly and/or indirectly by creating momentsthat oppose gravity) to provide support for structure 12.

The reinforcement may be pulled from head 16A as a result of head 16Abeing moved by support 14 away from an anchor point (e.g., away frompart holder 18). In particular, at the start of structure formation, alength of matrix-impregnated reinforcement may be pulled and/or pushedfrom head 16, deposited onto part holder 18, and cured, such that thedischarged material adheres (or is otherwise coupled) to part holder 18.Thereafter, head 16A may be moved away from part holder 18, and therelative movement may cause the reinforcement to be pulled from head16A. It should be noted that the movement of reinforcement through head16A could be assisted via internal feed mechanisms, if desired. However,the discharge rate of reinforcement from head 16A may primarily be theresult of relative movement between head 16A and part holder 18, suchthat tension is created within the reinforcement. As discussed above,part holder 18 could be moved away from head 16A instead of or inaddition to head 16A being moved away from part holder 18.

As can be seen in FIG. 1 , head 16A may include, among other things, anoutlet 24 and a matrix reservoir 26 located upstream of outlet 24. Inthis example, outlet 24 is a single-channel nozzle configured todischarge composite material having a generally circular, tubular, orrectangular cross-section. The configuration of head 16, however, mayallow outlet 24 to be swapped out for another outlet (not shown) thatdischarges composite material having a different shape (e.g., a flat orsheet-like cross-section, a multi-track cross-section, etc.). Fibers,tubes, and/or other reinforcements may pass through matrix reservoir 26and be wetted (e.g., at least partially coated and/or fully saturated)with matrix prior to discharge.

In the disclosed embodiment, a compactor 28 is located adjacent outlet24, and between outlet 24 and cure enhancer 23. It is contemplated,however, that the positions of compactor 28 and cure enhancer 23 may bereversed, if desired. It is also contemplated that more than onecompactor 28 may be utilized and organized in an alternating spatialarrangement relative to multiple cure enhancer(s) 23. Compactor 28 mayembody any type of device known in the art for compressing the compositematerial discharging from outlet 24 and/or for pressing the materialagainst a previously discharged layer of material. In the depictedexample, compactor 28 is a roller-type compactor that is biased (e.g.,via a spring—not shown) away from head 16A in an axial direction ofoutlet 24 and toward the discharging material. It is contemplated,however, that a shoe-type compactor, a skirt-type compactor, or anothertype of compactor could alternatively or additionally be utilized.Compactor 28 may be location- and/or pressure-adjustable, for examplevia an actuator (e.g., a hydraulic, pneumatic, and/or electric piston ormotor—not shown).

Head 16B of FIG. 1 may be an automated fiber placement (AFP) head. Head16B may include or otherwise be associated with a creel 30, on which anynumber of spools 32 may be mounted. Pre-impregnated reinforcements maybe fed from spools 32 through a collimator 34, which arranges thereinforcements into a tape having desired characteristics (e.g., width,thickness, composition, etc.). It should be noted that, in someembodiments, the reinforcements may already have a desired tape-form onspools 32, thereby obviating the need for collimator 34. The tape maypass near a warming mechanism (e.g., a heating coil or a light) 36 tosoften, melt, and/or otherwise tackify the tape, and then under asliding and/or rolling compactor 38 that presses the tape onto anunderlying surface (e.g., a surface of part holder 18, of structure 12,a support, or a surface of another adjacent structure). It should benoted that warming mechanism 36 may warm the tape prior to and/or onlyafter deposition, as desired. A cutting/clamping/feeding mechanism (notshown) could be disposed upstream of compactor 38, if desired, tofacilitate termination and/or restart of a printing operation.

FIG. 2 illustrates an alternative embodiment of head 16. In thisexample, a single head may include components common with heads 16A and16B that are integrated into a common package that together perform bothCF3D® and AFP operations. For instance, head 16 of FIG. 2 may include acommon base 40, to which cure enhancer(s) 23, outlet 24, matrixreservoir 26, compactor 28, creel 30, collimator 34, heating mechanism36, and/or compactor 38 are operatively mounted. Base 40 may beconnected to support 14, and head 16 of FIG. 2 may be activated toselectively dispense in-situ wetted reinforcements (e.g., via CF3D®components) and/or pre-impregnated reinforcements (e.g., via AFPcomponents).

In one example, both in-situ wetted reinforcements and pre-impregnatedreinforcements may be discharged at the same time. For example, outlet24 may dispense the in-situ wetted reinforcement (e.g., a functionalreinforcement such as a wire or an optical fiber), which is thereafterat least partially covered by a pre-impregnated reinforcement (e.g.,glass or carbon) pressed against the in-situ wetted reinforcement bycompactor 38. The covering of pre-impregnated reinforcement may functionas a protective, isolating, shielding, and/or dispersing cover for thefunctional reinforcement. In one example, the optical fiber may beactivated to illuminate desired portions of structure 12, and the glasscovering may protect the optical fiber from environmental conditionsand/or function to disperse light from the optical fiber in a desiredmanner.

In the above example, operation of cure enhancer(s) 23 and heatingmechanism 36 may be coordinated in several different ways. For example,cure enhancer(s) 23 may be selectively activated to only partially cure(e.g., cure to a B-stage) or to fully cure the in-situ wettedreinforcements prior to overlapping the in-situ wetted reinforcementswith the pre-impregnated reinforcements. It is also contemplated thatcure enhancer(s) 23 may not be activated at all and that the in-situwetted reinforcements are either completely uncured prior to overlappingor partially or fully cured via energy generated by heating mechanism36. In the latter example, it may be possible to completely eliminatecure enhancer(s) 23, if desired.

Similarly, operation of compactors 28 and 38 may be coordinated. Forexample, compactor 28 may be configured to compact the in-situ wettedreinforcements at a first pressure that is a percent of a secondpressure exerted by compactor 38 on the pre-impregnated reinforcement.Alternatively, compactor 28 may be completely eliminated and compactor38 may function to provide sole compaction of the in-situ andpre-impregnated reinforcements.

In some embodiments, a width of the pre-impregnated tape discharged overthe top of the in-situ wetted reinforcements may be different than awidth of the in-situ wetted reinforcements. For example, the tape widthmay be greater (e.g., multiple times greater), such that transverseedges of the tape extend past the in-situ wetted reinforcements and bondto structure 12 at the sides of and/or at a layer underlying the in-situwetted reinforcements. This may help to create a seal around the in-situwetted reinforcements.

In another embodiment of head 16, it is contemplated that thepre-impregnated reinforcements could be discharge through outlet 24, ifdesired. For example, the pre-impregnated reinforcements could be passedthrough matrix reservoir 26 where additional matrix is applied prior todischarge. Alternatively, the pre-impregnated reinforcements could bepassed through matrix reservoir 26 at a time when no matrix is presentin or advancing into reservoir 26, such that the pre-impregnatedreinforcements do not pick up any additional matrix. In yet anotheralternative, matrix reservoir could be modular and selectively removedduring discharge of the pre-impregnated reinforcements from outlet 24.In a final embodiment, the pre-impregnated reinforcements could bypassmatrix reservoir and enter outlet 24 at a downstream location. In any ofthese embodiments, it may be possible to eliminate heating mechanism 36and/or one of compactors 28 and 38. This may provide a more compact andinexpensive head 16.

When using head 16 of FIG. 2 to discharge composite material (i.e.,in-situ wetted reinforcement and/or pre-impregnated reinforcement),regulation of support 14 may need to be controlled differently dependingon the material(s) being discharged. In particular, head 16 may have twodifferent tool center points (shown as TCP in FIG. 2 ). Each TCP maycorrespond with a point or line of contact between an associatedcompactor (28 or 38) and structure 12, and support 14 may position head16 based on a known location of the TCP(s) currently being used inassociation with material discharge. For example, during discharge ofin-situ wetted reinforcement, the TCP location associated with compactor28 may be utilized to correctly position head 16. In another example,during discharge of pre-impregnated reinforcement, the TCP locationassociated with compactor 38 may be utilized to correctly position head16. And in a final example, when both in-situ and pre-impregnatedreinforcements are being discharged, the locations of both TCPs may betaken into consideration. The TCP(s) that should be considered whenposition head 16 may be determined based on a tool path predeterminedfor structure 12.

Referring back to FIG. 1 , a controller 42 may be provided andcommunicatively coupled with support(s) 14 and head(s) 16. Eachcontroller 42 may embody a single processor or multiple processors thatare configured to control an operation of system 10. Controller 42 mayinclude one or more general or special purpose processors ormicroprocessors. Controller 42 may further include or be associated witha memory for storing data such as, for example, design limits,performance characteristics, operational instructions, tool paths, andcorresponding parameters of each component of system 10. Various otherknown circuits may be associated with controller 42, including powersupply circuitry, signal-conditioning circuitry, solenoid drivercircuitry, communication circuitry, and other appropriate circuitry.Moreover, controller 42 may be capable of communicating with othercomponents of system 10 via wired and/or wireless transmission.

One or more maps may be stored in the memory of controller 42 and usedduring fabrication of structure 12. Each of these maps may include acollection of data in the form of lookup tables, graphs, and/orequations. In the disclosed embodiment, the maps may be used bycontroller 42 to determine the movements of heads 16 (e.g., thelocations of TCPs) required to produce desired geometry (e.g., size,shape, material composition, performance parameters, and/or contour) ofstructure 12, and to regulate operation of cure enhancer(s) 23,compactor 28, heating mechanism 36, compactor 38, and/or other relatedcomponents in coordination with the movements.

FIGS. 3, 4, 5A, and 5B illustrate examples of structures 12 that may befabricated via system 10. These figures will be discussed in more detailin the following section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed system may be used to manufacture composite structureshaving any desired cross-sectional shape and length. The compositestructures may include any number of different continuous fibers of thesame or different types and of the same or different diameters, and anynumber of different matrixes of the same or different makeup. Operationof system 10 will now be described in detail.

At a start of a manufacturing event, information regarding a desiredstructure 12 may be loaded into system 10 (e.g., into controller 42 thatis responsible for regulating operations of supports 14 and/or heads16). This information may include, among other things, a size (e.g.,diameter, wall thickness, length, etc.), a contour (e.g., a trajectory),surface features (e.g., ridge size, location, thickness, length; flangesize, location, thickness, length; etc.), connection geometry (e.g.,locations and sizes of couplings, tees, splices, etc.), functionalrequirements, matrix specifications (e.g., cure parameters),reinforcement specifications, etc. It should be noted that thisinformation may alternatively or additionally be loaded into system 10at different times and/or continuously during the manufacturing event,if desired. Based on the component information, one or more differentreinforcements and/or matrixes may be selectively installed and/orcontinuously supplied into system 10.

To install unimpregnated reinforcements into head 16A of FIG. 1 (and/orthe CF3D® portion of head 16 of FIG. 2 ), individual fibers, tows,and/or ribbons may be passed through matrix reservoir 26, through outlet24, past cure enhancer(s) 23, and under compactor 28 (i.e., betweencompactor 28 and an adjacent surface of structure 12 and/or part holder18). In some embodiments, the reinforcements may also need to beconnected to a pulling machine (not shown) and/or to a mounting fixture(e.g., to part holder 18). Installation of the matrix may includefilling head 16A (e.g., reservoir 26) and/or coupling of an extruder orother source of pressurized matrix (not shown) to head 16A.

To install pre-impregnated reinforcements into head 16B of FIG. 1(and/or the AFP portion of head 16 of FIG. 2 ), spools 32 of fibers,tows, and/or ribbons may be mounted to creel 30. The reinforcements maythen be fed and/or pulled through collimator 34, past heating mechanism36, and under compactor 38. In some embodiments, the reinforcements mayalso need to be connected to a pulling machine (not shown) and/or to amounting fixture (e.g., to part holder 18).

The component information may then be used to control operation ofsystem 10. For example, the in-situ wetted and/or pre-impregnatedreinforcements may be pulled and/or pushed from head(s) 16. Support(s)14 may also be controlled to selectively move head(s) 16 and/or platform20 (referring to FIG. 1 ) in a desired manner (e.g., based on knownpositions of TCP(s), known kinematics of support(s) 14, known positionof platform 20, and/or known geometry of structure 12) such that theresulting structure 12 is fabricated as desired. Operating parameters ofcure enhancer(s) 23, compactor 28, heating mechanism 36, compactor 38and/or other components of system 10 may be adjusted in real time duringmaterial discharge to provide for desired bonding, strength, and othercharacteristics of structure 12. Once structure 12 has grown to adesired length, structure 12 may be severed from system 10.

As shown in FIGS. 3 and 4 , AFP and CF3D® functions of head(s) 16 may beused together to fabricate unique aspects of structure 12. For example,CF3D® may be used to fabricate a permanent internal or externalstructure 44 that functions as a mold, core, and/or mandrel, over whichAFP may subsequently place a skin or outer surface 46 of pre-impregnatedreinforcements. In this example, cure enhancers 23 may only partiallycure the in-situ coated reinforcements (e.g., only enough to maintain adesired shape and size during subsequent tape application). After thetapes of pre-impregnated reinforcements have been placed onto the mold,core, and/or mandrel, the entire structure 12 may be placed into anautoclave for completion of the curing process. By only partially curingthe in-situ coated reinforcements, enhanced bonding between the in-situcoated reinforcements and pre-impregnated tapes may be realized duringautoclave curing of both the CF3D® and AFP fabricated portions ofstructure 12. In addition, a time required to complete structure 12 maybe reduced.

In some embodiments, an autoclave may not be needed at all. For example,it may be possible for head 16A and/or the CF3D® components of the FIG.2 —head 16 to discharge functional reinforcements (e.g., metallic wires,optical fibers, etc.) against surfaces previously placed by head 16Band/or the AFP portion of the FIG. 2 —head 16. Thereafter, thesefunctional reinforcements may be selectively energized to generate cureenergy directed toward the AFP-fabricated portions of structure 12,thereby causing these portions to cure. In another example, curing ofthe CF3D portions of structure 12 (e.g., when triggered via lightenergy) may result in a self-supporting exothermic reaction thatfunctions to initiate curing of and/or through-cure the AFP fabricatedportions of structure 12.

FIG. 3 illustrates an exemplary structure 12 made by combining thedifferent printing technologies, with CF3D® being used to fabricate ahoneycomb base that is then skinned via AFP. FIG. 4 illustrates acombination where CF3D® is used to make an internal honeycomb core,which is then covered on all sides with the tapes of pre-impregnatedreinforcements. It is contemplated that AFP may alternatively beutilized first to fabricate a shell or base layer of pre-impregnatedreinforcements, after which CF3D® is then used to fabricate structuresfrom in-situ wetted reinforcements and/or to lay functional fibers ontothe shell. As shown in FIGS. 3 and 4 , the pre-impregnated tapes mayinclude unidirectional reinforcements, woven reinforcements, or otherconfigurations of reinforcements.

The ability to selectively discharge in-situ and pre-impregnatedreinforcements with the same system 10 (and even the same head 16) mayhave many benefits. For example, normally expensive and/or permanent-usetooling (e.g., molds, inserts, etc.) may be replaced with cheaplyfabricated and quickly customized tooling. In addition, in place ofseparate standardized cores, unique cores that have been customized forparticular applications may be integrated with outer skins to formwell-bonded monolithic components. This may lightweight structure 12(e.g., by obviating the need for fasteners and/or reducing a density ofstructure 12), as well improve performance characteristics. Further,cheap durable pre-impregnated tapes may be used at locations wherehigh-volume material deposition and/or fine surface finishes arerequired, while fragile, lightweight, and/or expensive in-situ wettedreinforcements (e.g., structural and/or functional reinforcements) maybe utilized to enhance material properties and/or functionality atcritical locations with a high-degree of accuracy. In some applications,layers of pre-impregnated tapes may be interleafed with layers ofin-situ wetted reinforcements.

FIG. 5 illustrates one way that structure 44 may be fabricated. In thisexample, structure 44 is a honeycomb core, wherein generally identicalhexagonal prisms (“prisms”) 47 are fabricated adjacent each other as anintegral unit. Adjacent prisms 47 may be connected to each other via oneor more intersections 48. Because structure 12 may be fabricated by head16A of FIG. 1 or head 16 of FIG. 2 utilizing in-situ wettedreinforcements that are continuous, a layer-by-layer tool path around aborder of prisms 47 and through intersection(s) 48 may also becontinuous. During completion of each layer of prisms 47, a z-height ofprisms 47 may be increased by about one diameter of the wettedreinforcement. If the reinforcements were to cross each other at singlepoint associated with intersection 48, however, intersection 48 wouldincrease in z-height by about two diameters of the wetted reinforcementduring completion of each layer. In some applications, this could bedetrimental or unacceptable.

In order to maintain a z-height at intersection 48 that is about thesame (e.g., within engineering tolerances) as a border z-height ofprisms 47, care may be taken to cross reinforcements of differing layersat multiple locations. For example, when completing a first layer, thetool path may follow the dashed lines shown in FIG. 5B. And whencompleting a subsequent layer, the tool path may follow the solid linesshown in FIG. 5B. This may result in the in-situ wetted reinforcementscrossing each other at a total of four different locations 50. Duringfabrication of each new layer of adjacent prisms 47, the continuousreinforcement may cross itself only once within the same layer at afirst location 50. The continuous reinforcement may additionally cross alower-layer portion of itself only once and at a second location 50. Thefirst location may be oriented about 180 degrees from the secondlocation relative to a center of intersection 48. During fabrication ofa subsequent layer, the continuous reinforcement may again cross itselfonly once, but at a third location 50. The continuous reinforcement mayadditionally cross a lower-layer portion of itself only once and at afourth location 50. The third and fourth locations may be oriented about90 degrees from the first and second locations, respectively. In otherwords, the crossing locations may be different and alternate betweenadjacent layers. This alternating pattern may then be repeated as manytimes as required to produce a total desired z-height of structure 44.

Because each layer of the continuous reinforcement may cross itself onlyonce at a particular location 50 for every two layers that arefabricated, a z-height total at intersection 48 after fabrication of twoadjacent layers may be two diameters of the wetted reinforcement at anyone location. This should match the z-height total at the borders ofprisms 47 after fabrication of the two adjacent layers. In other words,following the pattern of FIG. 5A, prisms 47 should build up at theirborders at about the same rate as at their intersections 48. It shouldbe noted that structure 46 could have a shape (circles, ellipses,triangles, squares, etc.) other than hexagonal prisms 47, if desired.

It should be noted that, although FIGS. 5 and 5A show intersection 48 ashaving a general X-shape, it could have another shape if desired. Forexample, the reinforcements could arc into and/or out of crossing points50, thereby making intersection 48 generally circular. Other shapes arealso contemplated.

Further, it may be possible to cut and refeed the reinforcements atintersection 48, if desired. For example, during fabrication of a firstlayer, the reinforcement may pass directly through intersection 48.During a return of the reinforcement toward intersection 48, thereinforcement could be severed at a first side of intersection 48 andrestarted at the opposing side. While a discontinuous reinforcement mayhave a lower strength, the overall z-height at intersection 48 wouldbuild at a same rate as a z-height at a border of structures 44.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed system andmethods. Other embodiments will be apparent to those skilled in the artfrom consideration of the specification and practice of the disclosedsystem method. For example, although head 16 of FIG. 2 has beendescribed as having dual TCPs, each associated with a particularfabrication technology (e.g., CF3D® and AFP), it is contemplated thatother technologies could be combined with CF3D® in head 16. Forinstance, a fused deposition modeling (FDM), fused filament fabrication(FFF), and similar componentry may replace the AFP componentry and beused together with the CF3D® componentry. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

What is claimed is:
 1. A method of additively manufacturing a structure,comprising: discharging from a print head at least a first path ofmaterial to form a first layer of the structure; and discharging fromthe print head at least a second path of material to form a second layerof the structure, the second layer overlapping the first layer; wherein:the at least a first path of material crosses over itself at anintersection location within the first layer; the at least a second pathof material crosses over itself at the intersection location within thesecond layer; and a first trajectory of the at least a first path ofmaterial is different at the intersection location than a secondtrajectory of the at least a second path of material at the intersectionlocation.
 2. The method of claim 1, wherein the first and second layerstogether have a combined thickness that is constant at all locations. 3.The method of claim 2, wherein: the first layer has a thickness atnon-intersection locations that is equal to a thickness of the at leasta first path of material; the first layer has a thickness at theintersection location that is equal to twice the thickness of the atleast a first path of material; the second layer has a thickness atnon-intersection locations that is equal to a thickness of the at leasta second path of material; and the second layer has a thickness at theintersection location that is equal to twice the thickness of the atleast a second path of material.
 4. The method of claim 1, wherein: theintersection location within the first layer includes a first center;and the intersection location within the second layer includes a secondcenter that is coincident with the first center and offset in a layerthickness direction.
 5. The method of claim 4, wherein the firsttrajectory includes: a first portion passing through the intersectionlocation at a first side of the first center; and a second portionpassing through the intersection location.
 6. The method of claim 5,wherein the second portion passes through the intersection location at asecond side of the first center opposite the first side.
 7. The methodof claim 5, wherein the second trajectory is oriented relative to thefirst trajectory to form an X-shape at the intersection location.
 8. Themethod of claim 5, wherein the second trajectory includes a thirdportion passing through the intersection location that is orthogonal toat least the first portion.
 9. The method of claim 8, wherein the thirdportion is orthogonal to both the first and second portions.
 10. Themethod of claim 1, wherein the second trajectory is oriented relative tothe first trajectory to form an X-shape at the intersection location.11. The method of claim 1, wherein the at least a first path and the atleast a second path each includes a continuous fiber coated in a matrix.12. A method of additively manufacturing a structure, comprising:discharging from a print head at least a first path of material to forma first layer of the structure; and discharging from the print head atleast a second path of material to form a second layer of the structure,the second layer overlapping the first layer; wherein: the at least afirst path of material crosses over itself at an intersection locationwithin the second layer; the at least a second path of material crossesover itself at the intersection location within the second layer; andthe first and second layers together have a combined thickness that isconstant at all locations.
 13. The method of claim 12, wherein: thefirst layer has a thickness at non-intersection locations that is equalto a thickness of the at least a first path of material; and the firstlayer has a thickness at the intersection location that is equal totwice the thickness of the at least a first path of material.
 14. Themethod of claim 13, wherein: the second layer has a thickness atnon-intersection locations that is equal to a thickness of the at leasta second path of material; and the second layer has a thickness at theintersection location that is equal to twice the thickness of the atleast a second path of material.
 15. The method of claim 12, wherein:the intersection location within the first layer includes a firstcenter; and the intersection location within the second layer includes asecond center that is coincident with the first center and offset in alayer thickness direction.
 16. The method of claim 15, wherein the atleast a first path includes: a first portion passing through theintersection location at a first side of the first center; and a secondportion passing through the intersection location at a second side ofthe first center opposite the first side.
 17. The method of claim 16,wherein the at least a second path includes a third portion passingthrough the intersection location that is orthogonal to at least thefirst portion.
 18. The method of claim 12, wherein the at least a secondpath is oriented relative to the at least a first path to form anX-shape at the intersection location.